They labeled the phage DNA with radioactivePhosphorus-32. They then followed the phages while they infected E. coli. They found that the radioactive element left on the phage's DNA was only in the bacterium, and not in the phage, meaning that the DNA had entered the bacterium.

In a second experiment, Hershey and Chase put labels on the phage protein with radioactive Sulfur-35. After the phage was attached to the bacterium, the radioactive element was found in the phage, but not in the bacterium. This means that the phage's proteins stayed on the outside of the bacterium. These results showed Hershey and Chase that the genetic material that infects the bacteria is DNA.